On Fri, Jul 22, 2022 at 06:24:07PM +0800, ChiaEn Wu wrote:
> diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
> index a003e02..846dbe7 100644
> --- a/drivers/video/backlight/Kconfig
> +++ b/drivers/video/backlight/Kconfig
> @@ -268,6 +268,18 @@ config BACKLIGHT_MAX8925
> If you have a LCD backlight connected to the WLED output of MAX8925
> WLED output, say Y here to enable this driver.
>
> +config BACKLIGHT_MT6370
> + tristate "MediaTek MT6370 Backlight Driver"
> + depends on MFD_MT6370
> + help
> + This enables support for Mediatek MT6370 Backlight driver.
> + It's commonly used to drive the display WLED. There are 4 channels
> + inside, and each channel supports up to 30mA of current capability
> + with 2048 current steps in exponential or linear mapping curves.
Does the MT6372 support more steps than this? In other words does it use
a fourteen bit scale or does it use an 11-bit scale at a different
register location?
> +
> + This driver can also be built as a module. If so, the module
> + will be called "mt6370-backlight".
> +
> [...]
> diff --git a/drivers/video/backlight/mt6370-backlight.c b/drivers/video/backlight/mt6370-backlight.c
> new file mode 100644
> index 0000000..ba00a8f
> --- /dev/null
> +++ b/drivers/video/backlight/mt6370-backlight.c
> [...]
> +static int mt6370_bl_update_status(struct backlight_device *bl_dev)
> +{
> + struct mt6370_priv *priv = bl_get_data(bl_dev);
> + int brightness = backlight_get_brightness(bl_dev);
> + unsigned int enable_val;
> + u8 brightness_val[2];
> + int ret;
> +
> + if (brightness) {
> + brightness_val[0] = (brightness - 1) & MT6370_BL_DIM2_MASK;
> + brightness_val[1] = (brightness - 1) >> fls(MT6370_BL_DIM2_MASK);
> +
> + /*
> + * To make MT6372 using 14 bits to control the brightness
> + * backward compatible with 11 bits brightness control
> + * (like MT6370 and MT6371 do), we left shift the value
> + * and pad with 1 to remaining bits. Hence, the MT6372's
> + * backlight brightness will be almost the same as MT6370's
> + * and MT6371's.
> + */
> + if (priv->vid_type == MT6370_VID_6372) {
> + brightness_val[0] <<= MT6370_BL_DIM2_6372_SHIFT;
> + brightness_val[0] |= MT6370_BL_DUMMY_6372_MASK;
> + }
This somewhat depends on the answer to the first question above, but
what is the point of this shifting? If the range is 14-bit then the
driver should set max_brightness to 16384 and present the full range of
the MT6372 to the user.
Especially when using linear mappings (which are a totally pointless
scale to use for a backlight) the extra steps are useful for backlight
animation.
Daniel.
